Rebar Calculator for Footings

Last updated: 20 Sep 2025 | Author: Brij | Review By: Irshad

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Quickly calculate number of rebars, total length, and weight of steel required for concrete footings. Accurate and easy to use for construction projects.

Footing Length:

Footing Width:

meters

Rebar Spacing:

meters

Typically 0.15-0.3m (6-12 inches)

Rebar Diameter:

Common: 10, 12, 16, 20mm

Common Sizes:

Rebar Calculation Results

Longitudinal Rebars:

bars

Transverse Rebars:

bars

Total Rebar Length:

meters

Total Rebar Weight:

Rebar Calculation Information

Standard Practices:
- Minimum rebar diameter: 12mm for footings
- Maximum spacing: 300mm (12 inches)
- Concrete cover: 50mm (2 inches) assumed
- Standard lap lengths included in calculation

Calculation Formulas:
Bars in width direction = (Width / Spacing) + 1
Bars in length direction = (Length / Spacing) + 1
Weight (kg/m) = (Diameter²) / 162.2
Total weight = Total length × Weight per meter

Concrete footings are one of the most important structural elements in any building. To ensure strength and durability, reinforcing steel bars (rebars) are placed inside the footing. A Rebar Calculator for Footings helps you quickly estimate the number of rebars, total length, and total weight required for a rectangular footing.

What is a Rebar Calculator for Footings?

A rebar calculator for footings is a tool that allows you to:

Estimate the number of longitudinal rebars (length direction)
Estimate the number of transverse rebars (width direction)
Calculate the total length of steel required
Calculate the total weight of rebars

This ensures proper planning, cost estimation, and prevents wastage of material.

Formula for Number of Longitudinal Rebars

$N_L = \frac{W}{S} + 1$

Where:

$N_L$ = Number of longitudinal rebars
$W$ = Footing width
$S$ = Spacing of rebars

Formula for Number of Transverse Rebars

$N_T = \frac{L}{S} + 1$

Where:

$N_T$ = Number of transverse rebars
$L$ = Footing length
$S$ = Spacing of rebars

Formula for Total Length of Rebars

$L_{total} = (N_L \times L) + (N_T \times W)$

Where:

$L_{total}$ = Total length of rebars required

Formula for Weight of Rebars

Weight of rebar can be calculated using the contractor’s formula:

$W = \frac{d^2 \times L_{total}}{162}$

Where:

$W$ = Total weight of rebars (kg)
$d$ = Diameter of rebar (mm)
$L_{total}$ = Total length of rebars (m)

Example Calculation

Let’s calculate rebars for a footing of:

Length = 3 m
Width = 2 m
Spacing = 0.20 m (20 cm)
Rebar diameter = 12 mm

Step 1: Number of Longitudinal Rebars

$N_L = \frac{2}{0.20} + 1 = 11$

Step 2: Number of Transverse Rebars

$N_T = \frac{3}{0.20} + 1 = 16$

Step 3: Total Length of Rebars

$L_{total} = (11 \times 3) + (16 \times 2) = 65\ \text{m}$

Step 4: Weight of Rebars

$W = \frac{12^2 \times 65}{162} = 57.8\ \text{kg}$

So, for a 3 m × 2 m footing with 20 cm spacing and 12 mm bars, you need 65 m of rebar weighing about 57.8 kg.

Why Use a Rebar Calculator for Footings?

Saves time in manual steel estimation
Ensures accuracy in construction planning
Helps in budgeting material cost
Prevents shortage or wastage of steel

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